The present invention relates generally to stators for dynamoelectric machines and, in particular, to an stator assembly for a dynamoelectric machine including a core slot insert member.
Dynamoelectric machines, such as alternating current electric generators, or alternators, are well known. Prior art alternators typically include a stator assembly and a rotor assembly disposed in an alternator housing. The stator assembly is mounted to the housing and includes a generally cylindrically-shaped stator core having a plurality of axially-extending core slots formed therein. The core slots define a plurality of teeth therebetween. The teeth are connected to the core by a yoke portion. The rotor assembly includes a motor rotor attached to a generally cylindrical shaft that is rotatably mounted in the housing and is coaxial with the stator assembly. The stator assembly includes a plurality of wires wound thereon, forming windings. The stator windings are formed of straight portions that are located in the slots and end loop sections that connect two adjacent straight portions and are formed in a predetermined multi-phase (e.g. three or six) winding pattern in the slots of the stator core. The rotor assembly typically includes opposed poles as part of claw fingers having magnets that are positioned around an electrically charged rotor coil. The rotor coil produces a magnetic field. When a prime mover, such as a steam turbine, a gas turbine, or a drive belt from an automotive internal combustion engine, rotates the rotor assembly, the magnetic field of the rotor assembly passes through the stator windings, inducing an alternating electrical current in the stator windings, such as by magnetic flux from the rotor poles flowing from a pole of the rotor to the core teeth, through the core yoke and back to another opposite pole of the rotor. The alternating electrical current is then routed from the alternator to a distribution system for consumption by electrical devices or, in the case of an automotive alternator, to a rectifier and then to a charging system for an automobile battery. Although the “claw pole” rotor is described, those skilled in the art will recognize that the described stator design can be used in conjunction with other types of rotors, such as; permanent magnet non claw pole, permanent magnet claw pole, salient field wound and induction type rotors. It is known in the art that in order to increase the output and efficiency of an alternator it is desirable to have stator winding conductors of rectangular shaped cross sections that are aligned in a radial row in each core slot and whose widths, including any insulation, closely fit to the width, including any insulation, of the core slots. This is advantageous because the larger conductor width reduces the electrical resistance of the stator winding. It is also known in the art to provide a stator core with small slot openings at the inner diameter of the core, which results in more steel area on the inner diameter of the stator. The increased steel area increases the effective air gap area, which in turn increases alternator output. A smaller air gap also reduces the fluctuation of magnetic flux on the rotor pole surface which reduces eddy current losses and therefore increases alternator efficiencies. It is also desirable, however, to ease manufacturing of the stator winding by having continuous rectangular shaped conductors that are radially inserted through the core slot openings. These desirable features, however, lead to a design contradiction because the conductors that fit closely to the width of the core slot cannot be inserted into the core slot from a radially inward position through a smaller core opening.
Some prior art stator assemblies utilize continuous conductors that are small enough to enter the slot openings but disadvantageously do not closely fit the width of the slot. This design solution results in an alternator with low output and efficiency. Other prior art stator assemblies utilize a wing portion that extends radially from each of the teeth which is then bent circumferentially to narrow the gap between the teeth. The wing portions, however, disadvantageously tend to tear because they are attached to the core teeth and are difficult to control to the required inner diameter which is critical for alternator performance. Other prior art stator assemblies utilize hairpin conductors, in which U-shaped conductors are placed in the core slots from an upper or lower axial end of the stator core and not from a radially inward position. While these U-shaped conductors are advantageously rectangular and fit closely to the width of the core slots, the difficulty of manufacturing the stator winding is still increased because each of the opposing ends of the U-shaped conductors must be welded to form the stator winding.
It remains desirable to provide a stator assembly for an dynamoelectric machine that has high output and high efficiency while also being easy to assemble and manufacture. It is also desirable to provide an insert member for the core slots of an dynamoelectric machine stator to allow for a stator winding having conductors that fit closely to the width of the core slots and that allows the conductors to be inserted into the core slots from a radially inward position while also providing a smaller core opening.